Diabetes in Mid-Life Increases Alzheimer’s Risk

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May 27, 2008

Here’s yet one more reason to keep your weight down, eat healthy and exercise to avoid the onset of diabetes: Men who develop diabetes in mid-life significantly increased their risk of developing Alzheimer’s disease later, a new study from Sweden shows.

The long-term study, which lasted for some 35 years, found that men at age 50 who had abnormal levels of insulin, a hormone critical for controlling blood sugar that is linked to diabetes, were more than one-and-a-half times more likely than their healthy peers to develop Alzheimer’s disease years later. Men with insulin problems were also more likely to develop vascular dementia, a form of serious memory loss related to blood vessel damage in the brain. The findings were published in Neurology, the medical journal of the American Academy of Neurology.

Problems with insulin are a hallmark of diabetes. Produced by the pancreas, insulin regulates the uptake of blood sugar (glucose) by muscle and fat and is vital for normal body functioning. Many people who have diabetes must regularly inject themselves with a drug form of insulin because their bodies either do not make enough of the hormone or do not respond to it properly. In addition to those with diabetes, many people who are overweight or have high blood pressure or heart disease do not process insulin properly.

“Our results have important public health implications given the increasing numbers of people developing diabetes and the need for more powerful interventions,” said study author Dr. Elina Rönnemaa, M.D., of Uppsala University in Sweden.

Scientists hope that better understanding of the role of insulin in the development of Alzheimer’s may lead to new therapies to control, or even prevent, the mind-ravaging disease.

The study involved 2,269 men in Sweden who underwent glucose testing at age 50 to test for diabetes. During an average follow up of 32 years, 102 participants were diagnosed with Alzheimer’s disease, 57 with vascular dementia and 235 with other types of dementia or cognitive impairment.

Researchers found that the men with low insulin secretion capacity at age 50 were nearly one-and-a-half times more likely to develop Alzheimer’s disease than people without insulin problems. The risk remained significant regardless of blood pressure, cholesterol, weight and education level, other factors that have been linked to Alzheimer’s disease.

“Our results suggest a link between insulin problems and the origins of Alzheimer’s disease and emphasize the importance of insulin in normal brain function,” said Dr. Rönnemaa. “It’s possible that insulin problems damage blood vessels in the brain, which leads to memory problems and Alzheimer’s disease, but more research is needed to identify the exact mechanisms.”

A Growing Public Health Threat

About one in five people over age 65 has Type 2 diabetes, a chronic age-related ailment marked by poor control of blood sugar (glucose). Diabetes is especially common in older people who are overweight, though it is becoming increasingly common in younger persons as well. Weight control, including regular exercise and a healthy diet, are thought to be important in avoiding the onset of diabetes.

Previous research suggests that diabetes may increase Alzheimer’s risk through various possible pathways. For example, diabetes damages blood vessels in many parts of the body. It may affect blood vessels in the brain as well, impairing blood flow and damaging critical brain functions, including those involving memory.

High levels of insulin may lead to inflammation, too. Increasingly, researchers believe inflammation plays an important role in the health of the brain, heart, blood vessels and other vital body functions. High insulin has also been linked to high levels of beta amyloid. The buildup of toxic forms of beta amyloid in the brain is thought to play a key role in the development of Alzheimer’s. [See the article, “High Insulin Levels Linked to Alzheimer’s Disease“]

Stress hormones, too, may play a role in the link between Alzheimer’s and diabetes. People with poorly controlled diabetes often produce excess levels of a stress hormone called cortisol. Recently, scientists at the National Institutes of Health showed that rodents exposed to high levels of similar stress hormone have shrinkage of brain areas critical for learning and memory. [See the article, “Stress, Diabetes and Memory Loss“]

Millions of Americans have high insulin levels because of diabetes or as a result of a related metabolic condition sometimes called pre-diabetes. People who are overweight or have heart disease or high blood pressure also tend to produce greater amounts of insulin. As the population ages, more people are expected to suffer from these ailments, as well as from Alzheimer’s disease.

Other studies support the role of losing weight and maintaining a heart-healthy lifestyle in preventing the onset of diabetes and Alzheimer’s disease. Because these ailments are so common, greater understanding of insulin’s role in the development of Alzheimer’s is critical.

The Fisher Center for Alzheimer’s Research Foundation continues to fund critical research into the underlying causes of Alzheimer’s disease. To learn more, visit www.ALZinfo.org, The Alzheimer’s Information Site.

By www.ALZinfo.org, The Alzheimer’s Information Site. Reviewed by William J. Netzer, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.